In mediawiki-1.10.0 the option $wgDBport has no effect if $wgDBtype is "mysql".
Setting $wgDBport = "1234" (or any other value) has no offect on ability to
connect to database server.
$wgDBport was introduced for and used by Postgres since 1.7.

I believed that it is not possible to specify port for MySQL. I was wrong. The
"hostname:port" works.
If $wgDBserver = "hostname:port"; can be used (what about IPv6 addresses?) for
MySQL then it may be possible for PostgreSQL code to use it as well. Thet would
deprecate $wgDBport and close this bug.